A strange bug causes to spawn this weird chunks in your world with water starting always at Y: 63
It seems like a ocean tried to generate after the terrain itself was already done.
I can confirm this also happens without BOP.

I can't seem to reproduce this at all. Does this occur with TAN on its own?

Yes, the latest version to be precise

And did you test it without TAN?

yes, i did. I also used the same seed to make sure if it was gone and it was.

What is the seed you used?

For BOP I used -78688046
The location: X -87 Z 292

This bug seems to happen in any world type no matter what if you use TAN.

http://i.imgur.com/K0RHo1V.jpg

With Forge 1.9.4 - 12.17.0.1976, Biomes O' Plenty 1.9.4 - 4.1.0-2033 and Tough As Nails 1.0.3. All outside of eclipse. Would you be able to link your fml-client-latest.log file for when TAN is just on its own?

Also if you haven't already, update Forge

With BOP and TAN: http://pastebin.com/Ge59fT5q
With Other mods included: http://pastebin.com/tTby1Q5Q
TAN on its own: http://pastebin.com/gW4ky6jK

After changing the preferred Release type from Beta to Release in Curse, the problem seems to be fixed on it own somehow.

I spoke too soon...

The only other thing I could think of in that case then is try using the standard Vanilla launcher (Not the Curse launcher), with just TAN and Forge. Aside from that, there's nothing that stands out as out of the ordinary in those logs... I'm really not sure what to say here... Neither Forstride nor I can get this to happen which makes fixing it nigh impossible, especially since TAN doesn't touch terrain generation at all :(